1. Field of the Invention
This invention relates to passenger lifts and, in particular, it relates to an improved, hydraulically driven passenger lift with controlled movement during loading and storage operations.
2. Discussion of the Prior Art
An increasing sensitivity exists in our society for the mobility of people who have difficulty walking. Although various forms of wheelchairs have helped considerably, their users face many obstacles, as getting in and out of vehicles such as vans and buses. Consequently, there is a great need for improved passenger lifts having mobile platforms to raise and lower passengers effectively between a loading position, at ground level, and an entry position that is aligned with the vehicle's floor.
The convenience of passenger lifts is enhanced, if the platform folds or collapses for storage inside the vehicle. The speeds at which passenger lifts operate while moving through raising, lowering, stowing and deploying patterns gives rise to certain safety considerations. Based on such safety considerations, the Americans with Disabilities Act, 42 U.S.C. Sec. 1201 et seq., establishes a different limit on the speed at which wheelchair lift platforms can be raised or lowered, than the speed at which they can be deployed or stowed. Section 38.23(b)(10), Federal Register, Vol. 56, No. 173, p. 54757 provides that no part of the platforms shall move at a rate exceeding six inches/second while raising and lowering an occupant and shall not exceed twelve inches/second while deploying and stowing, unless the platforms are manually deployed or stowed. However, if swing motions are involved in deploying and storing platforms, further speed restrictions may be prudent. Typically, the raising and lowering or "up and down" operations must have the capability to operate with a substantial load, i.e. a person in a wheelchair. Conversely, the deploying and stowing operations involve only the weight of the lift.
U.S. Pat. No. 4,534,450 discloses a hydraulically driven passenger lift movable through loading, entry and storage patterns. The stated advantage of the hydraulic system of that patent is that the same pump raises the platform and powers its motions. The use of a single pump simplifies the system, thereby decreasing both the system's weight and cost while increasing the system's reliability.
However, a drawback of the hydraulic system of U.S. Pat. No. 4,534,450 is the difficulty of moving the platform at different speeds as it is stowed, deployed, raised and lowered. Consequently, a need exists for an economical, trouble-free, safe and convenient hydraulic lift with a flow control to move the lift platform at different speeds through patterns of deploying, loading and stowing.
Note that effective control of the platform speed as it is stowed and deployed may be particularly difficult due to load and power differences that occur. For example, the problem may be complicated by pressure differences occurring as the lift moves through different patterns. Consequently, there is a need for a hydraulic drive system for a passenger lift with a directionally dependent flow controlling device that is activated depending on the pattern of operation of the lift. Such a device would permit the lift platform to move at different speeds through different motion patterns.